1. Field of the Invention
The present invention relates to three-dimensional measuring machines (3D CMMs) used in metrology for measuring precision mechanical parts.
2. Description of the Related Art
These machines include a numerical control system of the type fitting out numerical control machine-tools (NCMTs), for numerically controlling a jointed arm. The arm bears a comparator and a feeler which is put into contact onto points of the surface to be measured, thereby located in a rectangular coordinate system of the theoretical reference system, or of the machine.
In order to perform the measurement or the inspection of a part; it is clamped on the measurement platen fitting out the CMM, and this accurately with respect to the machine or mechanical reference system. This reference system is embodied by a device of the platen, for example a reference surface, sphere or other surface, on which, during an initialization phase of the machine, the machine reference system is made to coincide with the reference system of the part to be measured before making it perform the measurements.
The feeler is then automatically and successively positioned by the machine on the points to be measured, and an operator simultaneously and manually notes down on the comparator the corresponding deviations with respect to the theoretical coordinates of these points.
This method is well suited for simple inspections of not very complex parts, when there are a few points to be checked or measured and when the number of parts to be measured is not too large.
However for complex parts such as blades of turbine engines, measurements are lengthy and the number of parts to be measured is significant. In this case, the method proves to be very costly.